An apparatus such as an electronic still camera recording a video signal of a still picture on a magnetic disk is commonly known in the art. An electronic still camera using a floppy disk having a diameter of about 47 mm and a thickness of about 40 .mu.m for recording has been standardized and put into practical use. The floppy disk is rotated at a rotational speed of 3,600 rpm, and fifty still pictures are recorded on fifty tracks in the case of field recording, while twenty-five still pictures are recorded on the fifty tracks in the case of frame recording. The track width and track pitch are 60 .mu.m and 100 .mu.m respectively, and a guard band having a width of 40 .mu.m is provided between the tracks. A reproduced picture is displayed on a monitor such as a television receiver or printed out as a hard copy by a printer.
In the record mode for recording an audio signal on such a floppy disk, the time base of the audio signal is compressed, while in the playback mode for reproducing the recorded audio signal from the floppy disk, the time base is expanded. This is because the floppy disk completes one revolution in a period of time of 1/60 sec, and an audio signal corresponding to this period of time can only be recorded on one track. However, when the time base in compressed by, for example, 1/640, the audio signal corresponding to an extended period of time of about 10 sec can be recorded on one track. Audio signals usually recorded on such a floppy disk include those of various sound frequency ranges such as oral explanation of recorded still pictures, background music recorded for observation of reproduced still pictures and background music recorded during photographing with an electronic still camera.
FIG. 3 shows diagrammatically the structure of an audio signal recording system, and FIG. 4 shows diagrammatically the structure of a video signal recording system.
As shown in FIG. 3, an audio signal 2 transmitted from a microphone 1 is applied to a time-base compressor 4 after being amplified by a signal processing unit 3. The time-base compressor 4 includes an A/D converter 5, a RAM (random access memory) 6, a D/A converter 7 and an address counter 10 and is designed to compress the time base by a factor of 1/640. Described in more detail, an audio output signal 3a of the signal processing unit 3 is sampled in the A/D converter 5 at a sampling frequency fs to be converted into a digital signal 5a. This digital signal 5a is written in the RAM 6 in synchronism with a clock signal having a frequency fs. For the purpose of writing, an address signal having a clock frequency fs is applied from the address counter 10 to the RAM 6. The digital signal written in the RAM 6 is read out from the RAM 6 in synchronism with a clock signal having a frequency of 640.times.fs and is converted by the D/A converter 7 into an analog signal 7a at a clock frequency of 640.times.fs.
The analog audio signal 7a compressed in the time base is applied from the D/A converter 7 to a frequency (FM) modulator 17 where the signal 7a is converted into an FM audio signal. The output signal of the FM modulator 17 is applied through a recording amplifier 18 to a magnetic head 8 to be recorded on a suitable track of a floppy disk 9. In this manner, the audio signal 2 transmitted from the microphone 1 is recorded on the floppy disk 9 in a form in which its time base is compressed by a factor of 1/640.
On the other hand, in the video signal recording system shown in a simplified form in FIG. 4, a video signal is processed in a signal processing unit 11 including a pre-emphasis circuit and an FM modulator, and the output signal of the signal processing circuit 11 is applied through a recording amplifier 12 to a magnetic head 13 to be recorded on a suitable track of the floppy disk 9. In FIG. 4, a gate opened by a record enable signal, is schematically illustrated as a switch 14.
In an electronic still camera in which a time base compressed audio signal is recorded together with a video signal of a still picture, there is a demand for recording audio information pertinent to the recorded video information. For example, in the case of recording a television signal, there is a demand for displaying a still picture in a matching relation with audio information which lasts for about 10 sec. This is because video information of a still picture corresponding to a period of time or only 1/60 sec is recorded, whereas audio information corresponding to a period of time as long as about 10 sec can be recorded due to the time-base compression. Thus, mismatching between the timing of reproducing the audio information and that of displaying the video information may sometimes occur.
It has been a common practice for a user of such an electronic still camera to select separate procedures for recording an audio signal and a video signal, the video signal being recorded at a timing different from the timing of recording the audio signal so as to attain matching between reproducing the audio information and displaying the video information. That is, the application of a start pulse to the address counter 10 shown in FIG. 3 and the application of a record enable signal to the gate 14 shown in FIG. 4 have been carried out separately. The above manner of manipulation has not necessarily been executed as scheduled, and mismanipulation has been inevitable. Further, the selection of the proper timing of recording the video signal with respect to the timing of recording the audio signal has been quite troublesome.